Department of Bioengineering.
Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
J Neurosci. 2018 Nov 21;38(47):10156-10167. doi: 10.1523/JNEUROSCI.0962-18.2018. Epub 2018 Oct 5.
The ability to interact with our environment requires the brain to transform spatially represented sensory signals into temporally encoded motor commands for appropriate control of the relevant effectors. For visually guided eye movements, or saccades, the superior colliculus (SC) is assumed to be the final stage of spatial representation, and instantaneous control of the movement is achieved through a rate code representation in the lower brain stem. We investigated whether SC activity in nonhuman primates (Macaca mulatta, 2 male and 1 female) also uses a dynamic rate code, in addition to the spatial representation. Noting that the kinematics of amplitude-matched movements exhibit trial-to-trial variability, we regressed instantaneous SC activity with instantaneous eye velocity and found a robust correlation throughout saccade duration. Peak correlation was tightly linked to time of peak velocity, the optimal efferent delay between SC activity and eye velocity was constant at ∼12 ms both at onset and during the saccade, and SC neurons with higher firing rates exhibited stronger correlations. Moreover, the strong correlative relationship and constant efferent delay observation were preserved when eye movement profiles were substantially altered by a blink-induced perturbation. These results indicate that the rate code of individual SC neurons can control instantaneous eye velocity and argue against a serial process of spatial-to-temporal transformation. They also motivated us to consider a new framework of saccade control that does not incorporate traditionally accepted elements, such as the comparator and resettable integrator, whose neural correlates have remained elusive. All movements exhibit time-varying features that are under instantaneous control of the innervating neural command. At what stage in the brain is dynamical control present? It is well known that, in the skeletomotor system, neurons in the motor cortex use dynamical control. In the oculomotor system, in contrast, instantaneous velocity control of saccadic eye movements is not thought to be enforced until the lower brainstem. Using correlations between residual signals across trials, we show that instantaneous control of saccade velocity is present earlier in the visuo-oculomotor neuraxis, at the level of superior colliculus. The results require us to consider alternate frameworks of the neural control of saccades.
与环境交互的能力要求大脑将空间表示的感觉信号转换为时间编码的运动指令，以对相关效应器进行适当的控制。对于视觉引导的眼球运动（或扫视），上丘（SC）被认为是空间表示的最后阶段，并且通过在下脑干中的速率码表示来实现运动的即时控制。我们研究了非人类灵长类动物（猕猴，2 只雄性和 1 只雌性）的 SC 活动是否也使用动态速率码，除了空间表示之外。注意到幅度匹配运动的运动学表现出试验间的可变性，我们将瞬时 SC 活动与瞬时眼速进行回归，发现整个扫视持续时间内存在稳健的相关性。峰值相关性与峰值速度紧密相关，在扫视开始和进行期间，SC 活动和眼速之间的最佳传出延迟均保持在约 12ms 不变，并且具有较高发射率的 SC 神经元表现出更强的相关性。此外，当眨眼引起的扰动极大地改变眼动曲线时，强烈的相关关系和恒定的传出延迟观察结果得以保留。这些结果表明，单个 SC 神经元的速率码可以控制瞬时眼速，并反对空间到时间转换的串行过程。它们还促使我们考虑一种新的扫视控制框架，该框架不包含传统上被认为的元素，例如比较器和可重置积分器，其神经相关性仍然难以捉摸。所有运动都表现出随时间变化的特征，这些特征受神经支配的神经命令的即时控制。大脑的哪个阶段存在动态控制？众所周知，在骨骼运动系统中，运动皮层中的神经元使用动态控制。相反，在眼球运动系统中，扫视眼运动的瞬时速度控制被认为直到下脑干才强制执行。通过跨试验的剩余信号之间的相关性，我们表明在视动神经轴上，在上丘水平，存在扫视速度的即时控制。结果要求我们考虑扫视神经控制的替代框架。
